Separation of mixtures with modified zeolites

ABSTRACT

An improved method for separation and isolation of individual components contained in a C8 aromatic mixture such as p-xylene and ethylbenzene, by contacting the mixture with an aluminosilicate zeolite which has been contacted with an organicradical substituted silane to modify the characteristics of the zeolite.

United States Patent Allen et al.

[ 1 SEPARATION OF MIXTURES WITH MODIFIED ZEOLITES I 72] Inventors: PaulT. Allen; B. M. Drinkard, both of Beaumont, Tex.

[73] Assignee: Mobil Oil Corporation [22] Filed: June 1, 1971 [2]] Appl.No.: 149,050

[56] References Cited UNITED STATES PATENTS 2,614,135 10/1952l-lirschler 2601674 3,653,l84 4/1972 Drinkard et al. ..55/67 3,658,6964/1972 Shively et al. ..208/3 10 3,656,278 4/1972 Drinkard et al. ..55/67 Primary Examiner-Delbert E. Gantz Assistant Examiner-C. E. SpresserAttorney-Oswald G. Hayes and Andrew L. Gaboriault- 571 ABSTRACT Animproved method for separation and isolation of individual componentscontained in a C aromatic mixture such as p-xylene and ethylbenzene, bycontacting the mixture with an aluminosilicate zeolite which has beencontacted with an organic-radical substituted silane to modify thecharacteristics of the zeolite.

24 Claims, No Drawings SEPARATION MIXTURES WITH ZEOLITES BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to thegas chromatographic separation of C aromatic mixtures and moreparticularly to a'ch romatographic method for the separation of amixture so as to recover essentially pure p-xylene and ethylbenzene inthe presence of a certain zeolite.

2. Description] of the Prior Art Gas chromatography, as a method for theseparation of mixtures of difficultly separable materials, has been wellknown for some time. in general, the method operates on the principle ofdistribution of the components of a sample over separate phases andsubsequent separation of these phases. For example, in gas-liquidchromatography, the volatile components of a sample are distributedbetween an inert gas phase (carrier gas) and a stationary liquid.Similarly in adsorption chromatography, there is obtained sampledistribution over a solid absorbent and a moving liquid phase. Columnspacked with the stationary liquid or solid adsorbent are usuallyemployed to effect the separations by passage of the mixture to beseparated therethrough. Hence, chromatography is a physical method ofseparation in which-the components to be separated are distributedbetween two phases, one of the phases constituting a stationary bed oflarge surface MODIFIED area, the other being a fluid that percolatesthrough or manufacture of synthetic fibers such as Dacron. The

ethylbenzene is also an important intermediate for making styrene bydehydrogenation. Normally they are separated from a product streamcontaining ethylbenzene, para-xylene, meta-xylene and ortho-xylene bycostly superfractionation and multistage refrigeration steps. Thisprocess involves high operation costs and has a limited yield.

it has also long been known that porous substances such as silica gel,activated char, and certain zeolites, have certain selective adsorptioncharacteristics useful in resolving a hydrocarbon mixture into itscomponent parts. Thus, silica gel is selective in removing aromatichydrocarbons from non-aromatic hydrocarbons and activated chars areuseful in separating olefins from mixtures with paraffins. Similarly,the molecular sieve properties of zeolites have been utilized toselectively remove one molecular species from a mixture of the same withother species.

Although a wide variety of zeolitic materials, particularly crystallinealuminosilicates, have been successfully employed in various separationschemes, nevertheless, these prior art processes, in general, fell intoone or two main categories. In one type, a zeolite is employed having apore size sufficiently large to admit the vast majority of componentsnormally found in a process stream. These molecular sieves are referredto as large pore zeolites and they are generallystated to have a poresize of about 13A such as zeolite X, Y, and L. The other type ofcrystalline aluminosilicates are those having a pore size ofapproximately 5A which are utilized to separate small molecules such asn-paraffins to the substantial exclusion of other molecular species. Thezeolites of these types, however; are not generally capable ofeffectively separating the close-boiling C aromatics. 1

Another proposed solution to this problem is set forth in U.S. Pat. No.3,126,425. This patent discloses contacting a mixtureof xylene isomerswith crystalline aluminosilicates such that the orthoand meta-isomersaresorbed by said aluminosilicates and the para-isomer is concentratedin the unabsorbed portion. This method is. concerned. with theconcentration of the more symmetrical disubstituted aromatic isomer,such as para-xylene, in the unadsorbed stream. it therefore apparentlyrepresents an extension of the normal relative partitioning of xyleneisomers with high surface area solids to the more selective crystallinealuminosilicate surface. All of the isomers described in the abovepatent will be sorbed by crystalline aluminosilicates having uniformpore openings of 10-13 Angstrom units. The separations shown aretherefore not dependent on the molecular sieving properties of the 13Angstrom zeolite, but rather, on the relative partitioning of the saidisomers between the intracrystalline sorbed phase and the free liquidphase. This method is therefore severely limited and may as stated berestricted because of economic considerations to processing only streamscontaining 50 percent or more para-xylene. The normal concentration ofparaxylene in equilibrium mixtures of xylene isomers obtained fromcommercial isomerization units is generally about 24 weight percent sothat this method will not accomplish the desired separation on feedssuch as this.

In still a later development by Applicants assignee, it was discoveredthat selective separations of this type can be achieved by utilizing aunique class of crystalline aluminosilicates which possess uniquemolecular sieving properties in that they allow entry and egress totheir internal pore structure of not only normal paraffins but also ofslightly branched paraffins and yet have the ability to effectivelyexclude paraffins possessing quaternary carbon atoms at short contacttimes. These zeolites also possess the ability to selectively sorbsimple, lightly-substituted monocyclic hydrocarbons from mixedhydrocarbon streams containing highly-substituted monocyclic,polycyclic, heterocyclic or even simple polycyclic hydrocarbons. Thesezeolites also possess the unique property of selectively sorbing 1,4

Ser. No. 44,459, now US. Pat. No. 3,653,184, both filed June 8, 1970 byB. M. Drinkard et al, there are disclosed gas chromatographicseparations of aromatic mixtures for the recovery of ethylbenzeneo-xylene, mxylene and p-xylene by contacting a C aromatic mixture with acertain crystalline zeolite to recover ethylbenzene, a mixture of mando-xylene and p-xylene and then separating the mand o-xylene over aliquid phase partitioning agent (44,460). In Ser. No. 44,459, themixture is first contacted with the partitioning agent to separateethylbenzene, o-xylene and a mixture of mand p-xylenes. The latter isthen separated over the zeolite. The crystalline aluminosilicatezeolites employed in the process of these copending applications aredisclosed as being ZSM-S and ZSM-8 zeolites.

In addition, in application Ser. No. 13,784 of George T. Kerr, entitled,ZEOLITE ESTERS, filed Feb. 24, 1970 of Applicants assignee, there aredisclosed as novel compositions of matter, crystalline aluminosilicateesters made by reacting a crystalline aluminosilicate having availablehydrogen atoms with an organic silane having an SiI-I group. Theresulting compositions are indicated as being useful for hydrocarbonconversion processes, particularly hydrocracking.

According to the present invention, it has been discovered that modifiedZSM-S and ZSM-8 type crystalline aluminosilicate zeolites, wherein saidmodification is carried out by contacting the zeolites with organicradical-substituted silanes provide unexpected and advantageous resultsin the gas chromatographic separation of the mixture of compoundscontained in a C aromatic feedstock.

SUMMARY OF THE INVENTION It is accordingly one object of the inventionto provide a process which overcomes or otherwise mitigates thedisadvantages of the prior art in this area.

A further object of the invention is to provide a chromatographicseparation process for the separation and isolation of mixtures ofcompounds contained in C aromatic mixtures.

A still further object is to provide a gas chromatographic separationprocess for the recovery of highly pure p-xylene and/or ethylbenzenefrom a C aromatic mixture employing in the chromatographic column amodified crystalline aluminosilicate zeolite.

Other objects and advantages of the present invention will becomeapparent as the description thereof proceeds.

In satisfaction of the foregoing objects and advantages there isprovided by this invention a process for the treatment of a C aromaticfeedstock for the recovery and isolation of substantially pure p-xylenein one embodiment, and p-xylene and ethylbenzene in a second aspect,which comprises contacting a C aromatic feedstock with a crystallinealuminosilicate which has been contacted with an organicradical-substituted silane. It has been found that a gas chromatographicseparation carried out in the presence of the modified zeolite disclosedherein results in a reduction of the mand o-xylene adsorption therebyimproving the product purity of p-xylene and ethylbenzene. In addition,the invention includes the concept of subsequently separating the m ando-xylene in a second column to effect a two-step process. Also providedare 4 the modified zeolites as formed by contacting of the crystallinealuminosilicates and the organic silane compounds.

DESCRIPTION OF THE PREFERRED EMBODIMENTS .column.

The modified zeolite compound employed in the process of the presentinvention, can be generally described as the reaction product of acrystalline aluminosilicate with an organic substituted silane. Theorganic substituted silanes deemed useful in the process of the presentinvention are those of the following general formula:

wherein, in the above formula R is an organic radical as describedhereinafter and each R is also an organic radical such as those definedbelow for the group R, a

. hydrogen atom or a halogen atom such as chlorine or bromine. Organicradicals which may be R or R include alkyl of l and more preferably upto about 40 carbon atoms, alkyl or aryl carboxylic acid acyl wherein theorganic portion of said acyl group contains about one to 30 carbon atomsand said aryl group con tains aboutsix to 24 carbon atoms, aryl groupsof about six to 24 carbons, which may also be further substituted,alkaryl and aralkyl groups containing about seven up to about 30 carbonatoms. Highly preferred compounds falling within the above structure arethose wherein R is alkyl of about 12 to 24 carbon atoms, i.e., the longchained alkyl groups, and each R is hydrogen or chlorine. Highlypreferred silanes are octadecyltrichlorosilane anddodecyltrichlorosilane. Organic silanes of the type useful in theprocess of the present invention are known in the art and may beprepared by known methods. For example, the tetrachloro substitutedsilane, SiCl may be prepared by the reaction of chlorine and silica andthe resulting product may then be reacted with the desired number ofmoles of a metal salt of the organic compound containing the radical forR or R desired, by heating. Other silanes employed in the process of thepresent invention may be prepared by similar procedures, all of whichare well known in the art.

The desired silane is then contacted with a zeolite of the typedescribed hereinafter, one requirement of the zeolite being that it havean available hydrogen for reaction. The silane should be selected sothat steric hindrance problems are avoided. Thus in the above formula, Rand only two R should be organic radicals which means that at least oneR should be halogen.

The selected silane and the crystalline aluminosilicate zeolite arecontacted in the preferred procedure at an elevated temperature.Preferably, the silane and zeolite are contacted on a weight basis ofabout 1:5 to 5:], preferably about 1:2 to 1:1, respectively. It is alsopreferable that a binder for the zeolite be employed such as, forexample, bentonite. For good contact between the reactants, it is alsopreferable to employ a reaction medium. Satisfactory reaction mediainclude the ethers, aliphatic hydrocarbons and halo-substitutedaliphatic hydrocarbons of .5 to about 8 carbon atoms, (e.g.,n-h'eptane), the aromatic, halo-substituted aromatic hydrocarbons andnitrogen containing compounds such as heterocyclics. A particularlypreferred media is pyridine.

As indicated, an elevated temperature should also be employed for thereaction, preferably a temperature of about 75 to 200 C. A convenientprocedure is to charge the reactants to the medium and heat at thereflux point of the system for about 1 to 10 hours. The mixture is thencontacted with a volatile solvent such as chloroform or n-pentane,filtered and dried in an oven at a temperature of about 75 to 125 C.

The resulting modified zeolite may be described as a crystallinealuminosilicate having the organic substituted silane chemically bondedthereto and the resulting zeolite is thermally stable.

As has been stated, the separation process of this invention is achromatographic one. This is intended to describe a process whereinseparation is based on selective adsorption of at least one component ofa mixture by a-solid. The solid is the modified zeolite previouslydescribed.

Thenovel chromatographic separation process of this invention is carriedbut merely by contacting the hydrocarbon mixture described, existingeither as a gas, liquid or mixed phase with the modified crystallinezeolite such thatthe desired component is concentrated in either thesorbed or non-sorbed phase. A suitable fluid carrier can be employed ifsuch is desired. Typical carriers include polar and non-polar compoundssuch as nitrogen, air, steam, water, hydrogen, hydrocarbons, helium,etc. The process can be carried out in either a batch or a continuousoperation. The sorbed material can be subsequently recovered byconventional desorbing techniques such as thermal stripping, strippingwith an inert gas, e.g., nitrogen, helium, etc. or evacuation ofelutriation with a suitable polar or non-polar stripping agent, e.g.,water, n-hexane, etc.

In general, the process of the invention utilizes a chromatographicseparation of the mixture of ethylbenzene, ortho-xylene, meta-xylene,and para-xylene into its component parts. This mixture, which isgenerally a feed reformate from a commercial unit, either as a gas,liquid or mixed phase, is preferably contacted with the carrier and thencontacted with the modified zeolite. Conveniently, contact with thezeolite is carried out in .a column, that is, the zeolite is maintainedin a column and the feed/carrier mixture is passed therethrough. Theseparated components are then recovered on elution.

In one embodiment of the process of the invention, the C aromatic feedmixture would contain about up to 15 weight percent of ethylbenzene,about 20 to 30 weight percent of paraxylene, about 40 to 50 weightpercent of meta-xylene and about 15 to 25 weight percent ofortho-xylene. In this embodiment, contact of this mixture with thezeolite would first separate a mixture of the meta-xylene andortho-xylene'followed by the para-xylene and then the ethylbenzene. Inthis procedure, adsorption of the mand o-xylene is substantiallyreduced.

In a second embodiment of the process, the C arematic feed mixturestarting material contains no or very little ethyl-benzene and aseparation of p-xylene in high purity is effected. In this embodiment,aC mixture of m-, oand p-xylene-and is admixed with a carrier andcontacted with the modified zeolite. There is initially eluted a mixtureof the mand o-xylene followed by very pure xylene.

Generally in practicing the process, the modified zeolite is packed intoa column and the feedstock is fed therethrough. In typical liquid phasechromatography, the products are recovered from the column by elutionwith a liquid such as an organic solvent. In typical vapor phaseoperations, the products are eluted from the column by carrier gas.

In a further main embodiment of the process, the mixture of m-xylene andortho-xylene from the modified zeolite column can also be separated bygas chromatographic separation over a chromatographic liquid phasepartitioning agent in a second column. Thus in this procedure, atwo-column system is set up, a first column containing the zeolite esterand a second column containing the liquid partitioning agent. Ingeneral, the column containing the liquid partitioning agent oradsorbent is about twenty times larger in volume than thezeolite-containing column, although this may be varied depending onother conditions of the process.

In this second step of the process, the mixture of ortho-xylene andmeta-xylene, initially eluted from the zeolite-containing column, isthen. transmitted through the second column containing the standardliquid partitioning phase substance together with the carrier. In thiscolumn the two components of this mixture are separated to provideinitially the meta-xylene in 99 percent purity and thereafter theortho-xylene in 99 percent purity, both in substantially quantitivefields. In this column, the meta-xylene is sorbed at a slower rate thanthe ortho-xylene. Thus from this mixture the process provides means forrecovery of all the valuable components in highly purified form.

In conducting the reaction the C aromatic feed would be contacted with agaseous carrier, preferably helium or steam, although others may beused, and passed through the chromatographic column containing themodified crystalline aluminosilicates. As the mixture passes through thecolumn, it has been found that, quite unexpectedly, the modificationperformed on the zeolite has the effect of reducing the mand oxyleneadsorption, as measured by peak tailing, and

thereby improves p-xylene and ethylbenzene product purity. Thus, sinceadsorption of the mand oxylene is reduced over the modified zeolite, themand o-xylene mixture passes through the zeolite-packed column recoveredas the first elutant, it is then separated in the second column. In thesecond column, there is maintained a gas-liquid chromatographic medium,ordinarily employed for separation of components as they pass through acolumn with a carrier gas. A preferred material as this type is knowncommercially as Tergitol NPX (nonyl phenol ether of polyethyleneglycol). However, equivalent materials may also be employed withsubstantially the same results. Such materials are, for example, m-bis(m-phenoxy-phenoxy) benzene 2 percent squalane; UCON 1540 or UCONLB-550X, sold under those tradenames by Union Carbide Corporation;di-n-propyl tetrachlorophthalate; squalane; 40 percent 1,2,3 tris(2-cyanoethoxy) propane 60 percent oxybis (2ethyl benzoate); anddi-n-decylphthalate. Obviously, equivalent materials may also be used.In general, however, the second column may be said to contain anystationary phase liquid partitioning agent as known in thechromatographic art.

The temperature at which the separations are carried out is important.Thus, the novel process of this invention can be carried out attemperatures ranging from about 100 C. to about 250 C. It should benoted that a wider temperature range can be employed but because of thepossibility of catalytic conversion in the zeolitecontaining column, 250C. appears to be a suitable upper limit. A more preferred temperaturerange appears to be between about 100 to 200 C. It is noted that theabove temperatures might vary slightly depending upon the particularcationic form of the crystalline aluminosilicate zeolite employed but,in general, they represent operable parameters for carryin g out thenovel process of this invention.

There may, of course, be used any of the active aluminosilicate zeolitesknown to the art for reaction with the silanes and use in the process ofthis invention. However, the class of aluminosilicates known as ZSM-5zeolites and described hereinafter are highly preferred.

As indicated above, the zeolites utilized in the column are of a specialtype and are disclosed and claimed for use in a novel zeolitechromatographic process in copending Application Ser. No. 882,692, filedDec. 5, 1969, .l. Cattanach of the same assignee. Generally, thesezeolitic materials allow selective separations to be achieved dependingon either the size, shape or polarity of the sorbate molecules. Thisclass of novel crystalline aluminosilicates can generally be stated tohave intermediate shape-selective sorption properties. The unique natureof this novel class of zeolites is characterized by the presence ofuniform pore openings which are apparently'elliptical rather thancircular in nature. The effective pore openings of this unique class ofzeolites have both a major and minor axis, and it is for this reasonthat the unusual and novel molecular sieving effects are achieved. Theunique type of molecular sieving produced has generally been referred toas a keyhole molecular sieving action. From their dynamic molecularsieving properties it would appear that the major and minor axis of theelliptical pore in this family of zeolites have effective sizes of about7.0 i 0.7A and 5.0 i 0.5A, respectively.

This general family of zeolites are described as ZSM- 5 typecompositions. In general, they have the characteristic X-ray diffractionpattern set forth in Table 1 hereinbelow. ZSM-5 compositions can also beidentified, in terms of mole ratios of oxides, as follows:

wherein M is a cation, n is the valence of said cation, W is selectedfrom the group consisting of aluminum and gallium, Y is selected fromthe group consisting of silicon and germanium, and Z is from O to 40. Ina more preferred synthesized form, the zeolite has a formula, in termsof mole ratios of oxides, as follows:

and M. is selected from the group consisting of a mixture of alkalimetal cations, especially sodium, and tetraalkylammonium cations, thealkyl groups of which preferably contain two to five carbon atoms.

In a preferred embodiment of ZSM-5, W is aluminum, Y is silicon and thesilica/alumina mole ratio is at least 10 and ranges up to about 60.

Members of the family of ZSM-5 zeolites possess a definitedistinguishing crystalline structure whose X- ray diffraction patternshows the significant lines set forth in Table 1 following:

TABLE 1 Interplanar Spacing d(A) Relative Intensity 11.1 i 0.2 S 10.0:0.2 S 7.4 i 0.15 W 7.1 i 0.15 W 6.3 i 0.1 W 6.04t 0.1 W 5.97 i 0.1 W5.56 i 0.1 W 5 01 i 0.1. W 4.60 0.08 W 4.25 0.08 W 3.85 i 0.07 VS 3.71:t 0.05 S 3.64 t 0.05 M 3.04i 0.03 W 2.99 i 0.02 W 2.94 i 0.02 W

These values as well as all other X-ray data were determined bystandard. techniques. The radiation was the K-alpha doublet of copper,and a scintillation counter spectrometer with a strip chart pen recorderwas used. The peak heights, 1, and the positions as a function of 2times theta, where theta is the Bragg angle, were read from thespectrometer chart. From these, the relative intensities, Ill, where Iis the intensity of the strongest line or peak, and d (obs.), theinterplanar spacing in A, corresponding to the recorded lines, werecalculated. In Table l the relative intensities are given in terms ofthe symbols S strong, M medium, MS medium strong, MW medium weak and VSvery strong. It should be understood that this X-ray diffraction patternis characteristic of all the species of ZSM- compositions. Ion exchangeof the sodium ion with other cations reveals substantially the samepattern with some minor shifts in interplanar spacing and variation inrelative intensity. Other minor variations can occur depending on thesilicon to aluminum ratio of the particular sample, as well as if it hadbeen subjected to thermal treatment. Various cation exchanged forms ofZSM-5 have been prepared. X-ray powder diffraction patterns of severalof these forms are set forth below in Table 2. The ZSM-S forms set forthbelow are all aluminosilicates.

TABLE 2 X-Ray Diffraction ZSM-S Powder-in Cation Exchanged Forms dSpacmgs Observed Made HCI NaCl CaCl RECl AgNO Zeolite ZSM-S can besuitably prepared by preparing a solution containing tetrapropylammonium hydroxide, sodium oxide, an oxide of aluminum or gallium, anoxide of silica or germanium, and water and having a composition, interms of mole ratios of oxides, falling wherein R is propyl, W isaluminum or gallium and Y is silicon or germanium, maintaining themixture until crystals 61 1161661116 are formed. Thereafter, the,

crystals are separated from the liquid and recovered. Typical reactionconditions consist of heating the foregoing reaction mixture to atemperature of from about to 200 C for a period of time of from about 6hours to 60 days. A more preferred temperature range is from about to Cwith the amount of time at a temperature in such range being from about12 hours to 8 days.

The digestion of the gel particles is carried out until crystals form.The solid product is separated from the reaction medium, as by coolingthe whole to room temperature, filtering, and water washing.

The foregoing product is dried, e.g., at 230 F, for from about 8 to 24hours. Of course, milder conditions may be employed if desired, e.g.,room temperature under vacuum.

ZSM-5 is preferably formed as an aluminosilicate. The composition can beprepared utilizing materials which supply the appropriate oxide. Suchcompositions include for an aluminosilicate, sodium aluminate, alumina,sodium silicate, silica hydrosol, silica gel, silicic acid, sodiumhydroxide and tetrapropylammonium hydroxide. It will be understood thateach oxide component utilized in the reaction mixture for preparing amember of the ZSM-5 family can be supplied by one or more initialreactants and they can be mixed together in any order. For example,sodium oxide can be supplied by an aqueous solution of sodium hydroxide,or by an aqueous solution of sodium silicate; tetrapropylammonium cationcan be supplied by the bromide salt. The reaction mixture can beprepared either batchwise or continuously. Crystal size andcrystallization time of the ZSM-S composition will vary with the natureof the reaction mixture employed. The family of ZSM-5 zeolites isdisclosed and claimed in copending application Ser. No. 865,472, filedOct. 10, 1969, of Applicants assignee.

Another operable zeolite falling within the above class and useful inthe process of the invention is zeolite ZSM-8 which is described andclaimed in Ser. No. 865,418, filed Oct. 10, 1969, of Applicantsassignee.

The ZSM-8 family can also be identified, in terms of mole ratios ofoxides, as follows:

wherein M is at least one cation, n is the valence thereof and z is fromto 40. in a preferred synthesized form, the zeolite has a formula, interms of mole ratios of oxides, as follows:

and M is selected from the group consisting of a mixture of alkali metalcations, especially sodium, and tetraethylammonium cations.

ZSM-8 possesses a definite distinguishing crystalline structure havingthe following X-ray diffraction pattern:

TABLE 4 dA 1 16 1/16 dA Zeolite ZSM-8 can be suitably prepared byreacting a solution containing either tetraethylammonium hydroxide ortetraethylammonium bromide together with sodium oxide, aluminum oxide,and an oxide of silica and water. i

The relative operable proportions of the various ingredients have notbeen fully determined and it is to be immediately understood that notany and all proportions of reactants will operate to produce the desiredzeolite. In fact, completely different zeolites can be preparedutilizing the same starting materials depending upon their relativeconcentration and reaction conditions as is set forth in US. Pat. No.3,308,069. In general, however, it has been found that whentetraethylammonium hydroxide is employed, ZSM-8 can be prepared fromsaid hydroxide, sodium oxide, aluminum oxide, silica and water byreacting said materials in such proportions that the forming solutionhas a composition in terms of mole ratios of oxides falling within thefollowing range SiO /Al O from about 10 to about 200 NaO/tetraethylammonium hydroxide from about 0.05 to 0.20Tetraethylammonium hydroxide/SiO from about 0.08 to 1.0

H Oltetraethylammonium hydroxide from about to about 200 Thereafter, thecrystals are separated from the liquid and recovered. Typical reactionconditions consist of heating the foregoing reaction mixture to atemperature of from about to 175 C for a period of time of from about 6hours to 60 days. A more preferred temperature range is from about to Cwith the amount of time at a temperature in such range being from about12 hours to 8 days.

The digestion of the gel particles is carried out until crystals form.The solid product is separated from the reaction medium, as by coolingthe whole to room temperature, filtering, and water washing.

The foregoing product is dried, e.g., at 230 F, for from about 8 to 24hours. Of course, milder conditions may be employed if desired, e.g.,room temperature under vacuum.

ZSM-S is prepared utilizing materials which supply the appropriateoxide. Such compositions include sodium aluminate, alumina, sodiumsilicate, silica hydrosol, silica gel, silicic acid, sodium hydroxideand tetraethylammonium hydroxide. It will be understood that each oxidecomponent utilized in the reaction mixture can be supplied by one ormore initial reactants and they can be mixed together in any order. Forexample, sodium oxide can be supplied by an aqueous solution of sodiumhydroxide, or by an aqueous solution of sodium silicate,tetraethylammonium cation can be supplied by the bromide salt. Thereaction mixture can be prepared either batchwise or continuously.

The zeolites used in the instant, invention can have the originalcations associated therewith replaced by a wide variety of other cationsaccording to techniques well known in the art. Typical replacing cationswould include hydrogen, ammonium and metal cations including mixtures ofthe same.

Typical ion exchange techniques would be to contact the particularzeolite with a salt of the desired replacing cation or cations. Althougha wide variety of salts can Representative ion exchange techniques aredisclosed in a wide variety of patents including US. Pat.

No. 3,140,249; US. Pat. No. 3,140,251; and U.S. Pat. No. 3,140,253.

Following contact with the salt solution of the desired replacingcation, the zeolites are then preferably washed with water and dried ata temperature ranging from 150 F to about'600 F and thereafter calcinedin air or other inert gas at temperatures ranging from about 500 to l500F for periods of time ranging from 1 to 48 hours or more.

Prior to use, the zeolites should be dehydrated at least partially. Thiscan be done by heating to a temperature in the range of 200 to 600 C. inan atmosphere, such as air, nitrogen, etc. and at atmospheric' orsubatmospheric pressures for between 1 and 48 hours. Dehydration canalso be performed at lower temperatures merely by using a vacuum, but alonger time is required to obtain a sufficient amount of dehydration.

ln practicing the process, it may be desired to incorporate the zeolitewith another material resistant to the temperatures and other conditionsemployed in the separation processes. Such matrix materials includesynthetic or naturally occurring substances as well as inorganicmaterials such as clay, silica and/or metal oxides. The latter may beeither naturally occurring or in the form of gelatinous precipitates orgels including mixtures of silica and metal oxides.

Naturally occurring clays which can be composited with the zeolitesinclude the montmorillonite and kaolin family, which families includethe subbentonites, and the kaolins commonly known as DixieMcNamee-Georgia and Florida clays or others in which the main mineralconstituent is halloysite, kaolinite, dickite, nacrite, or anauxite.Such clays can be used in the raw state as originally mined or initiallysubjected to calcination, acid treatment or chemical modification.

well as ternary compositions such as silicaaluminathoria,silica-alumina-zirconia, silica-alumina-magnesia andsilica-magnesia-zirconia. The matrix can be in the form of a cogel. Therelative proportions of finely divided crystalline aluminosilicate ZSM-Sand inorganic oxide gel'matrix vary widely with the crystallinealuminosilicate content ranging from about 1 to about 99 percent byweight and more usually, particularly when the composite is prepared inthe form of beads in the range of about 40 to about 90 percent by weightof the composite.

Another embodiment of thisinvention resides in subjecting the zeoliteZSM-S-type to a mild steam treat ment carried out at elevatedtemperatures of 800 to l500 F. and preferably at temperatures of about1000 to 1400 F. The treatment may be accomplished in an atmosphere of100 percent steam, or in atmosphere consisting of steam and a gas whichis substantially inert to the aluminosilicate. Thesteam treatmentapparently provides beneficial properties in the aluminosilicatecompositions andcan be conducted before, after or in place of thecalcination treatment.

The carriers which may be'employed are discussed hereinabove. Also,theprocess may be carried out in either a batch or continuous operation.The sorbed material can be subsequently recovered by conventionaldesorbing techniques such as thermal stripping, stripping with an inertgas, e.g., nitrogen, helium, etc.

or evacuation or elutriation with a suitable polar or non-polarstripping agent, e.g., water, n-hexane, etc.

The following examples will illustrate the best mode contemplated forcarrying out the present invention.

EXAMPLES 14 Typical preparations of ZSM-5 type zeolites are shown inthese examples. Examples 1-3 show the preparation of the hydrogen formZSM-S and they involve the use of tetrapropyl-ammonium hydroxide (T-PAOH) or bromide (TPABr). Example 4 shows a typical preparation of thehydrogen form ZSM-8 using tetraethyl ammonium hydroxide (TEACH).Reaction conditions and results are shown in Table 5.

TABLE 5 30 g. NaAlO; 281g. Sorbeadfines. 0.6611). NflAlOz.. 13 g.NilAlOz. 720 g. Ludox 3.3 lb. 'IPABr solutlon 44.7 lb. Q-brand... 300 g.TEAOH. Rooooioo composition if iiilfftifii::11:ijjijjjijjjjjijijiijjiiah fiffitbifiii ifnb i illziox.

Reaction temperature C.) 150 Time (hr.) 16

Washed, dried at 230 F., calcined 16 hrs. at 1,00D F.

NH C1 solution Base Exchange:

Cone. (wt. percent) Temp. C.)

In addition to the foregoing materials, theZSM-S type zeolites can becomposited with a porous matrix material such as silica-alumina,silica-magnesia, silicazirconia, silica-thoria, silica-beryllia,silica-titania as EXAMPLE 5 In this example 30 parts of a ZSM-Scrystalline alumino-silicate zeolite of the type prepared in Examplesl-4 comprising parts ZSM-S and 20 parts bentonite binder, were refluxedwith octadeclytrichlorosilane in a weight ratio of 1:1 in 200 ccnormal-heptane solvent for a period of four hours. Thereafter theresulting solid product was .recovered by decantation, the solid washedfirst with chloroform, then with normal-pentane and then dried at atemperature of 125 C. for 4 hours.

EXAMPLE 6 ln this example 20 grams of the zeolite prepared in accordancewith Example was packed into a gas chromatographic column maintained ata temperature of 180 C. and employed in a C aromatic separation. Thefeedstock was pumped to the top of the zeolite chromatographic column ata pumping speed of 4 ml. per hour and there admixed with carrier steampumped at a rate of 25 ml. per hour. The feedstock contained 15 weightpercent ethylbenzene, 18 weight percent pxylene, 4 l weight percentm-xylene, and 26 weight percent o-xylene. The mixture was then allowedto pass through the chromatographic column containing thesurface-modified zeolite. Fractions were eluted from the column using ahelium flow and steam as a stripping agent. After about two minutes thefirst fraction recovered was a mixture of o-xylene and m-xylene.Thereafter, in the period of about three to five minutes there waseluted p-xylene following in the period of five to eight minutes,ethylbenzene. The p-xylene and ethylbenzene products recovered showed apurity of greater than 98 percent at a throughput of 0.2 lb.feed/hr./lb/ of packing. Also, as measured by peak tailing, surfaceadsorption of the mand ortho-xylene was substantially reduced.

EXAMPLE 7 The process of Example 6 was repeated except that there wasmaintained in the column a ZSM-5 zeolite of the same type but which hadnot been contacted with the octadecyltrichlorosilane. The results showedthe recovery of the p-xylene fraction of a purity of only about 87percent and a throughput of 0.2 lb. feed/hr./lb. of packing thusdemonstrating the efficiency of the use of the silane-modified zeolites.

EXAMPLE 8 In this example, there is illustrated the embodiment ofseparating the ethylbenzene, p-xylene, m-xylene and o-xylene into itscomponent parts utilizing a zeolitecontaining column and a second columncontaining a liquid partitioning agent. Thus in this example, a firstcolumn eleven inches long and 0.5 inches in diameter was packed with 20grams of ZSM-5 zeolite prepared in accordance with the procedure ofExample 5 and maintained at 180 C. A second column 10 feet long and 0.50inches in diameter was provided containing Tergitol NPX on Chromosorb P.The feed was 0.6 ml of a reformate of the following composition:

ethylbenzene weight percent para-xylene 18 weight percent meta-xylene 42weight percent ortho-xylene 25 weight percent This mixture was pumped tothe top of the first column (zeolite) at a pumping speed of 4 ml/hr andthere admixed with steam, pumped at a rate of 25 ml/hr in a vaporizer.The mixture was then passed through the zeolite-containing column.Fractions were eluted from the column using a steam flow as a strippingagent. After one minute the first fraction was recovered which was 0.4ml of a mixture of ortho-xylene and meta-xylene.

In the period of 5-6 minutes, there was eluted 0.11 ml of para-xylenewhich analysis showed had a purity of 98 percent. Then, in the period of7-9 minutes, 0.09 ml of ethylbenzene was eluted which analysis indicatedhad a purity of 98 percent.

The 0.40 ml mixture of orthoand meta-xylene was then passed to the topof the second column for contact with the Tergitol NPX. Fractions wereeluted from the bottom of this column in the same manner. From thiscolumn, in the period of 9-12 minutes, 0.25 ml of meta-xylene was elutedwhich analyzed as 99 percent pure and in the period of 13-14 minutes,0.15 ml of 99 percent pure ortho-xylene was eluted. Recovery of eachcomponent was essentially 100 percent.

This specific working example illustrates the process as being carriedout utilizing two separate columns, one containing the ODTCS contactedzeolite and the other containing the partitioning agent. Quiteobviously, however, the separation procedure could also be effected in asingle-stage column or chromatographic process which could containcombinations of the separation media. Thus in this em'bodimnet,'a singlecolumn would be utilized with the column containing the ODTCS contactedzeolite as the first separation medium and the partitioning agent as thesecond separation medium. Also, the technique of Example 8 can also beemployed in the embodiment of Example 10.

EXAMPLE 9 This example illustrates preparation of a zeolite ester. Inthis preparation 80 parts 60-80 mesh ZSM-5 zeolite in admixture with 20parts bentonite binder were mixed with octadecyltrichlorosilane in aweight ratio of 1:5, respectively, placed in 200 cc n-heptane andrefluxed for four hours. Then the mixture was decanted, washed withchloroform and n-pentane and dried at C. for four hours.

EXAMPLE 10 In this example 20 grams of the zeolite prepared inaccordance with Example 9 was packed into a chromatographic columnmaintained at ambient temperature and employed in a C aromaticseparation. The feedstock contained 30 weight percent p-xylene, 50weight percent m-xylene and 20 weight percent 0- ,xylene. Six ml of thefeedstock was pumped to the top of the zeolite chromatographic columnand was then allowed to pass through the chromatographic columncontaining the ODTCS contacted zeolite. The mixture of mand o-xylene wasthen removed by washing with pseudocumene. Thereafter the p-xylene wasrecovered by eluting with n-heptane. The p-xylene recovered in thisexample was a purity of 99 percent, thus being of sufficient purity forterephthalic acid manufacture. The alkyl groups chemically bonded to thesurface of the ZSM-S particles essentially eliminated mand o-xylenesorption but did not appear to greatly affect p-xylene sorptionproperties.

The invention has been described herein with reference to certainpreferred embodiments. However, it is not to be considered as limitedthereto as obvious variations thereon will become apparent to thoseskilled in the art.

We claim:

1. A process for the separation of a C aromatic mixture for the recoveryof the para-xylene therefrom which comprises contacting. said mixturewith a modified zeoliteformed by the reaction of a crystalline zeolitematerial with an organic radical-substituted silane of the formula;

' R-Si-Rt wherein R is an organic radial and each R is an organicradical the same as R, hydrogen or a halogen atom, provided that atleast one R, is halogen, by contacting said mixture with said modifiedzeolite, whereby said components are sorbed at different respectiverates by said modifiedzeolite and recovering the para-xylene.

2. A process according to claim 1 wherein the zeolite is selected fromthe group consisting of ZSM- type zeolites having the X-ray diffractionpattern of Table l, ZSM-8 zeolites having the X-ray diffraction patternof Table 4 and mixtures thereof.

3. A process according to claim 2 wherein the modified zeolite ismaintained in a column maintained at an elevated temperature, and saidmixture and a carrier is passed therethrough for separation and recoveryof the products.

4. A process according to claim 3 wherein said carrier is selected fromthe group consisting of steam, water, nitrogen, air, helium, hydrogen,hydrocarbons and mix tures thereof. 1

5. A process according to claim 4 wherein the temperature maintained inthe column ranges from about 100 to about 250 C.

6. A process according to claim 5 wherein the C aromatics feed mixturecontains ethylbenzene, paraxylene, meta-xylene and ortho-xylene andwherein a mixture of the meta-xylene and ortho-xylene is initiallyremoved from the column followed by the para-xylene and then theethylbenzene.

7. A process according to claim 5 wherein the C aromatics feed mixturecontains para-xylene, meta-xylene, and ortho-xylene and wherein amixture of meta-xylene and ortho-xylene is initially removed from thecolumn followed by the para-xylene.

8. A process according to claim 2 wherein, in preparation of themodified zeolite, the zeolite and silane are reacted in weight ratios ofabout 5:1 to 1:5, respectively, in the presence of an organic solvent.

9..A process according to claim 8 wherein the organic solvent ispyridine and the reaction is carried out at a temperature of about 75 to200 C.

10. A process according to claim 9 wherein the silane compound is of theformula:

wherein R is an alkyl group of 1 to about 40 carbon atoms, an alkyl oraryl acyl groupwhere the organic portion of said alkyl group containsabout one to 30 carbon atoms, and of said aryl group contains about sixto 24 carbon atoms, aryl groups of about six to 24 carbon atoms, alkaryland aralkyl groups containing about seven up to about 30 carbon atomsand each R is the same as R, hydrogen, or a halogen atom, providing thatno more than one R, is the same as Rand at least one R, is halogen.

11. A process according to claim 10 wherein said zeolite and said silaneare reacted in the presence of a binder for said zeolite by refluxing ina 3:1 to 1:3 weight ratio in n-heptane solvent.

12. A process according to claim 11 wherein said zeolite is selectedfrom the group consisting of ZSM-5 type zeolites having the X raydiffraction pattern of Table l, ZSM-8 type zeolites having the X-raydiffraci t R-Si-Ri wherein R is an organic radical and R is an organicradical, hydrogen or halogen, provided that at least one R is halogen,by passing said C aromatic mixture in contact with said modified zeolitewhereby any mixture of meta-xylene and ortho-xylene passes through themodified zeolite rather uninhibited while any ethylbenzene andpara-xylene are sorbed at different respective rates by the modifiedzeolite, removing a mixture of meta-xylene and ortho-xylene, recoveringparaxylene followed by recovery of ethylbenzene, if the latter ispresent in the C aromatic mixture, passing the mixture of meta-xyleneand ortho-xylene into contact with a partitioning liquid whereby saidmeta-xylene and ortho-xylene are separated by sorption at differentrates and recovering the meta-xylene followed by the ortho'xylene.

14. A process according to claim 13 wherein the zeolite is a ZSM-S typezeolite having the X-ray diffraction pattern of Table l, a ZSM-8 typezeolite having the X-ray diffraction pattern of Table 4 or mixturesthereof.

15. A process according to claim 14 wherein the C aromatic feed mixturecontains about 0 to 15 weight percent ethylbenzene, about 20 to 30weight percent para-xylene, about 40 to 50 weight percent metaxylene andabout 15 to 25 weight percent ortho-xylene.

16. A process according to claim 15 wherein, in preparation of themodified zeolite, the zeolite and silane are reacted in weight ratios ofabout 5:1 to 1:5 in the presence of an organic solvent.

17. A process according to claim 16 wherein the organic solvent ispyridine and the reaction is carried out at a temperature of about to200 C.

18. A process according to claim 17 wherein the silane compound is acompound of the formula:

R-Si-Ri wherein R is an alkyl group of one to about 40 carbon atoms, analkyl or aryl acyl group where the organic portion of said alkyl groupcontains about one to 30 carbon atoms, and of said aryl group containsabout six to 24 carbon atoms, aryl groups of about six to 24 carbonatoms, alkaryl and aralkyl groups containing about seven up to about 30carbon atoms, and each R is the same as R, hydrogen or halogen atoms,providing that no more than one R, is the same as R and at least one R,is halogen.

19. A process according to claim 18 wherein said zeolite and said silaneare reacted in the presence of a binder for said zeolite by heating in a1:2 to 1:1 weight ratio in an organic solvent.

20. A process according to claim 19 wherein said partitioning liquid isselected from the group consisting of Terigtol NPX (nonyl phenol etherof polyethylene glycol), m-bis (m-phenoxy-phenoxy) benzene and 2 percentsqualane, UCON 1840, UCON LB-SSOX, di-npropyl tetrachlorophthalate,squalane, 40 percent 1,2,3 tris (2-cyanoetho'xy) propane and 70 percentoxybis (2-ethylbenzoate) and di-n-decylphthalate.

21. A process according to claim 20 wherein the zeolite and partitioningliquid are maintained in columns through which the mixture is passed ata temperature of about 100 to 250 C. v I

22. A process according to claim 21 wherein the column containing theliquid has a volume about twenty times greater than the zeolite column.

23. A process according to claim 22 wherein a carrier is admixed withthe mixture prior to passage through the columns and wherein the carrieris selected from the group consisting of steams, water, nitrogen, air,

2. A process according to claim 1 wherein the zeolite is selected fromthe group consisting of ZSM-5 type zeolites having the X-ray diffractionpattern of Table 1, ZSM-8 zeolites having the X-ray diffraction patternof Table 4 and mixtures thereof.
 3. A process according to claim 2wherein the modified zeolite is maintained in a column maintained at anelevated temperature, and said mixture and a carrier is passedtherethrough for separation and recovery of the products.
 4. A processaccording to claim 3 wherein said carrier is selected from the groupconsisting of steam, water, nitrogen, air, helium, hydrogen,hydrocarbons and mixtures thereof.
 5. A process according to claim 4wherein the temperature maintained in the column ranges from about 100*to about 250* C.
 6. A process according to claim 5 wherein the C8aromatics feed mixture contains ethylbenzene, para-xylene, meta-xyleneand ortho-xylene and wherein a mixture of the meta-xylene andortho-xylene is initially removed from the column followed by thepara-xylene and then the ethylbenzene.
 7. A process according to claim 5wherein the C8 aromatics feed mixture contains para-xylene, meta-xylene,and ortho-xylene and wherein a mixture of meta-xylene and ortho-xyleneis initially removed from the column followed by the para-xylene.
 8. Aprocess according to claim 2 wherein, in preparation of the modifiedzeolite, the zeolite and silane are reacted in weight ratios of about5:1 to 1:5, respectively, in the presence of an organic solvent.
 9. Aprocess according to claim 8 wherein the organic solvent is pyridine andthe reaction is carried out at a temperature of about 75* to 200* C. 10.A process according to claim 9 wherein the silane compound is of theformula: wherein R is an alkyl group of 1 to about 40 carbon atoms, analkyl or aryl acyl group where the organic portion of said alkyl groupcontains about one to 30 carbon atoms, and of said aryl group containsabout six to 24 carbon atoms, aryl groups of about six to 24 carbonatoms, alkaryl and aralkyl groups containing about seven up to about 30carbon atoms and each R1 is the same as R, hydrOgen, or a halogen atom,providing that no more than one R1 is the same as R and at least one R1is halogen.
 11. A process according to claim 10 wherein said zeolite andsaid silane are reacted in the presence of a binder for said zeolite byrefluxing in a 3:1 to 1:3 weight ratio in n-heptane solvent.
 12. Aprocess according to claim 11 wherein said zeolite is selected from thegroup consisting of ZSM-5 type zeolites having the X-ray diffractionpattern of Table 1, ZSM-8 type zeolites having the X-ray diffractionpattern of Table 4 and mixtures thereof.
 13. A process for theseparation of a C8 aromatic mixture feedstock into its component partswhich comprises contacting said mixture with a modified zeolite which isthe reaction product of a crystalline zeolite with an organicradical-substituted silane of the formula: wherein R is an organicradical and R1 is an organic radical, hydrogen or halogen, provided thatat least one R1 is halogen, by passing said C8 aromatic mixture incontact with said modified zeolite whereby any mixture of meta-xyleneand ortho-xylene passes through the modified zeolite rather uninhibitedwhile any ethylbenzene and para-xylene are sorbed at differentrespective rates by the modified zeolite, removing a mixture ofmeta-xylene and ortho-xylene, recovering para-xylene followed byrecovery of ethylbenzene, if the latter is present in the C8 aromaticmixture, passing the mixture of meta-xylene and ortho-xylene intocontact with a partitioning liquid whereby said meta-xylene andortho-xylene are separated by sorption at different rates and recoveringthe meta-xylene followed by the ortho-xylene.
 14. A process according toclaim 13 wherein the zeolite is a ZSM-5 type zeolite having the X-raydiffraction pattern of Table 1, a ZSM-8 type zeolite having the X-raydiffraction pattern of Table 4 or mixtures thereof.
 15. A processaccording to claim 14 wherein the C8 aromatic feed mixture containsabout 0 to 15 weight percent ethylbenzene, about 20 to 30 weight percentpara-xylene, about 40 to 50 weight percent meta-xylene and about 15 to25 weight percent ortho-xylene.
 16. A process according to claim 15wherein, in preparation of the modified zeolite, the zeolite and silaneare reacted in weight ratios of about 5:1 to 1:5 in the presence of anorganic solvent.
 17. A process according to claim 16 wherein the organicsolvent is pyridine and the reaction is carried out at a temperature ofabout 75* to 200* C.
 18. A process according to claim 17 wherein thesilane compound is a compound of the formula: wherein R is an alkylgroup of one to about 40 carbon atoms, an alkyl or aryl acyl group wherethe organic portion of said alkyl group contains about one to 30 carbonatoms, and of said aryl group contains about six to 24 carbon atoms,aryl groups of about six to 24 carbon atoms, alkaryl and aralkyl groupscontaining about seven up to about 30 carbon atoms, and each R1 is thesame as R, hydrogen or halogen atoms, providing that no more than one R1is the same as R and at least one R1 is halogen.
 19. A process accordingto claim 18 wherein said zeolite and said silane are reacted in thepresence of a binder for said zeolite by heating in a 1:2 to 1:1 weightratio in an organic solvent.
 20. A process according to claim 19 whereinsaid partitioning liquid is selected from the group consisting ofTerigtol NPX (nonyl phenol ether of polyethylene glycol), m-bis(m-phenoxy-phenoxy) benzene and 2 percent squalane, UCON 1840, UCONLB-550X, di-n-propyl tetrachlorophthalate, squalane, 40 percent 1,2,3tris (2-cyanoethoxy) propane and 70 percent oxybis (2-ethylbenzoate) anddi-n-decylphthalate.
 21. A process according to claim 20 wherein thezeolite and partitioning liquid are maintained in columns through whichthe mixture is passed at a temperature of about 100* to 250* C.
 22. Aprocess according to claim 21 wherein the column containing the liquidhas a volume about twenty times greater than the zeolite column.
 23. Aprocess according to claim 22 wherein a carrier is admixed with themixture prior to passage through the columns and wherein the carrier isselected from the group consisting of steams, water, nitrogen, air,helium, hydrogen, hydrocarbons and mixtures thereof.
 24. A processaccording to claim 23 wherein the zeolite is selected from the groupconsisting of ZSM-5 and ZSM-8 and the partitioning liquid is TergitolNPX.